// Invert a binary tree.
// 
//      4
//    /   \
//   2     7
//  / \   / \
// 1   3 6   9
// to
//      4
//    /   \
//   7     2
//  / \   / \
// 9   6 3   1
// Trivia:
// This problem was inspired by this original tweet by Max Howell:
// // Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so fuck off.

 /////Definition for a binary tree node.
 
 
 struct TreeNode {
     int val;
     TreeNode *left;
    TreeNode *right;
     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 };

class Solution {
public:
    TreeNode* invertTree(TreeNode* root)
	{  
        if(!root)
        return NULL; 
        
		TreeNode* node;
        node = root->left;
        root->left = root->right;
        root->right = node;
        
        if(root->left != NULL) 
		{
            invertTree(root->left);
        }
        
        if(root->right != NULL) 
		{
            invertTree(root->right);
        }
        
        return root;
        
    }
};